It is known to equip motor vehicles with tire-pressure monitoring systems. These systems generally comprise a device fixed to the inside of the tire and called a wheel unit. This wheel unit measures the pressure inside the tire (and also a certain number of other parameters such as, for example, the temperature) and transmits the measurements made to a central computer located in the vehicle. This central computer is responsible for warning the driver of any pressure defect in one of the tires. Of course, each wheel unit is provided with an identifier so that the data received by the central computer not only contains the measurements made but also an indication of position of tire (right or left front tire, right or left rear tire) in which these measurements have been made.
It is also known to transmit the data, measured by the suitable sensors located in the wheel units, at different time intervals depending on the movement of the vehicle. If the vehicle is in parking mode, that is to say at rest or moving at very slow speed (for example less than 25 km/h), the measurements made by the wheel units are generally transmitted at relatively long time intervals (of around one hour). On the other hand, when the vehicle is in running mode, that is to say moving at more than 25 km/h, the same information is transmitted to the central processing unit at time intervals of around one minute.
As soon as the vehicle is in running mode, each wheel unit regularly transmits the measurements made. However, many transmission are thus made simultaneously by several wheel units of one and the same vehicle. This results in scrambling of the messages received by the central processing unit that collects the transmissions coming, sometimes simultaneously, from the four wheels (or even more in the case of heavy goods vehicles). In this case, the data measured can no longer be used and the system becomes inoperable.
To overcome these drawbacks, it is known to time-shift the transmission of each wheel unit. These time-shifting methods are complex as they require all the wheel units of one and the same vehicle to be synchronized. Furthermore, this requires complex computations that limit the time intervals available for transmission.
To overcome this problem of collision between data transmitted by each wheel unit, it is also possible to ensure that the central computer interrogates each of the wheel units one by one. However, here again, this operating mode extends the time required to receive all the data and slows down the performance of the tire-pressure monitoring system.